STREPTOCOCCUS PYOGENES. 481 
posure, two hours): Mercuric chloride, 1 : 2500; sul- 
phate of copper, 1: 200; trichloride of iodine, 1 : 750; 
peroxide of hydrogen, | : 50; carbolic acid, 1: 300; 
eresol, 1: 250; lysol, 1: 300; creolin, 1: 130. 
Pathogenesis. The majority of test animals are not 
. very susceptible to infection by the streptococcus, and, 
hence, it is difficult to obtain any definite pathological 
alterations in their tissues through the inoculation into 
them of cultures of this organism by any of the methods 
ordinarily practised. White mice and rabbits, under 
similar conditions, are the most susceptible, and these 
animals are, therefore, usually employed for experimen- 
tation. Streptococci, however, differ greatly in the 
effects which they produce in inoculated animals, 
according to their animal virulence, which is very 
different from human virulence. The most virulent, 
when injected in the minutest quantity into the circu- 
lation or into the subcutaneous tissues of a mouse or 
rabbit, produce death by septicemia. Those of some- 
what less virulence produce the same result when in- 
jected in considerable quantities. Those still less patho- 
genic produce septicemia, which may be mild or severe, 
when injected into the circulation; but when injected 
subcutaneously, they produce abscess or erysipelas. 
The remaining streptococci, unless introduced in quan- 
tities of 20 c.c. or over, produce only a slight redness, 
or no reaction at all, when injected subcutaneously, 
and little or no effect when injected directly into the 
circulation. Many of the streptococci obtained from 
cases of cellulitis, abscess, empyema, and even septi- 
cemia belong to this group. 
A number of varieties of streptococci have thus been 
discovered, differing in virulence and in their growth 
31 
